A patient addicted to insulin must get plural injections of insulin per week or day. A required amount of insulin varies from patient to patient. A required amount of insulin for each patient varies from injection to injection, and it also varies from day to day.
A patient who performs injection by himself attaches a drug cartridge containing a drug to an injector, and attaches a needle assembly to an elastic seal of the drug cartridge, and thereafter, sets a dose, and operates the injector to inject the drug into his body. The drug in the drug cartridge runs out when such administration is performed a few times. The patient detaches an empty drug cartridge from the injector, and attaches a new drug cartridge to repeat the above-mentioned injection. As for a conventional injector, when the drug cartridge is replaced with a new cartridge, a member that holds the drug cartridge (hereinafter referred to as a cartridge holder) is detached from a body of the injector, and the drug cartridge is detached from the cartridge holder. Then, a new drug cartridge is inserted into the cartridge holder, and thereafter, the cartridge holder is attached to the injector (for example, see Japanese Utility Model Registration No. 3088706).
Although the above-mentioned conventional injector is a hand-operated injector, there is a motor-operated injector as shown in FIG. 24. FIG. 24 is a diagram illustrating inner structure of a motor-operated injector which is currently popular for dental use. A principle of drug administration will be described with reference to FIG. 24. A syringe 203 filled with a drug is set in a cartridge holder 202 attached to a body 210.
When a switch SW1 is pressed, a motor 211 rotates forward, and a rotational force is decelerated by a deceleration gear box 209 that is directly connected to the motor 211, whereby a deceleration gear main shaft 208 of the deceleration gear box 209 is rotated. An end of the deceleration gear main shaft 208 is engaged with a gear 206 via a rotation plank 207, whereby the gear 206 is rotated. Further, since the gear 206 is engaged with a gear 205, a rotational force of the gear 206 propagates to the gear 205. A gear 205a is located coaxially with the gear 205 so as to be engaged with a rack 204a that is provided on a lower right half of an extrusion piston 204. When the gear 205 rotates, the gear 205a also rotates in the same direction as the gear 205, and consequently, the extrusion piston 204 moves toward an injection needle 213, whereby drug in the syringe 203 is pressed out of the injection needle 213.
During injection, after performing air releasing in the above-mentioned operation, the injection needle 213 is inserted into a target area, and the drug is administered. In FIG. 24, SW2 denotes a switch for rotating the motor 211 in a reverse order, and 212 denotes a battery for driving the motor 211.
Further, it is very important for an insulin injector to be portable, and therefore, a compact and light-weight injector is desired. The conventional injector is generally provided with a linear piston having a stroke that enables injection of all drug in the drug cartridge. However, there is an injector provided with a curvature type piston (for example, see Japanese Published Patent Application No. 2000-513974).
By the way, when a patient actually uses an injector, the patient desires easy replacement of drug cartridges.
In the conventional injector, however, the patient must detach the cartridge holder into which the drug cartridge is inserted from the body of the injector, detach the drug cartridge from the cartridge holder, attach a new drug cartridge to the holder, and mount the cartridge holder onto the injector body, resulting in an inconvenient and troublesome operation.
Further, in a case of the injector having a linear piston, the piston must have a stroke that enables injection of all drug in the drug cartridge, and a length of the piston becomes approximately equal to an entire length of the drug cartridge. Therefore, a length of the injector itself becomes at least two times as long as the drug cartridge, leading to an increase in a size of the injector. Further, in a case of the injector having a curvature type piston, a length of the injector becomes shorter than that of the linear piston rod. However, since the piston has a curvature, a thickness of the injector is increased, leading to a disadvantage in handleability.
Furthermore, in the conventional administration apparatus for medical use shown in FIG. 24, although operation is easy because drug injection is motor-operated, the patient might be anxious as to whether or not the motor-operated injector including a drive mechanism such as a motor is normally operated. An act of drug administration itself provides mental stress to the patient, and furthermore, abnormal operation of the motor-operated injector greatly affects a human body, which may endanger the life of the patient.
The conventional administration apparatus for medical use is constructed as described above, and operation of cartridge replacement is troublesome.
Further, a size of the apparatus is too large to handle.
Furthermore, as for the motor-operated apparatus, the patient might be anxious during drug administration about air releasing before injection, an operation state of a mechanism, or the like.